Technical Field
The present invention relates to a photoelectric encoder.
Related Art
Conventionally, a photoelectric encoder including a scale having a scale pattern, and a detection head that moves along the scale and detects a relative movement amount with the scale is known. The detection head includes a light emitting unit for irradiating with a light beam toward the scale, and a detection unit for detecting interference fringes generated by being diffracted by the scale to output an electric signal, and the relative movement amount is calculated based on the electric signal output from the detection unit.
Incremental (INC) type and absolute (ABS) type are known as a type of detecting the relative movement amount of such a photoelectric encoder. The INC type continuously detects incremental (INC) patterns provided on the scale at a constant pitch, and detects a relative position by counting up or counting down the number of graduations of the passed INC patterns. The ABS type detects absolute (ABS) patterns randomly provided on the scale at an appropriate timing, and detects absolute positions by analyzing the ABS patterns.
The photoelectric encoder includes one using either one of the INC type or the ABS type, and one using the INC-ABS combined type of using a juxtaposed scale of the INC pattern and the ABS pattern. However, the INC-ABS combined type has a problem that since the INC pattern and the ABS pattern juxtaposed in the transverse direction of the scale are detected by using respective different detection units, when the attitude of the detection head is displaced or undulation occurs in the scale, an error occurs in the position information detected by the detection unit. Thus, a position encoder (photoelectric encoder) using hybrid INC-ABS integrated scale patterns combining the INC patterns and the ABS patterns with a series of scale patterns has been proposed (see, for example, Japanese Patent No. 4008356).